1. Field of the Invention
The present invention relates to a device for reducing the relative humidity of a flowing gas which is warmer than ambient air, such as gas expired by a living subject, of the type having an inlet, a container filled with a hydrophilic material, and a flow channel for the flowing gas, the flow channel passing through the container to dehumidify the flowing gas, and an outlet.
2. Description of the Prior Art
Air (gas) expired by a person is generally saturated with water vapor and has a relatively high temperature, about 33.degree.-34.degree. C. In many situations, expired air is subjected to different measurements, e.g., during the ventilation of a patient, administration of anesthesia or specimen-taking. Measurements can concern, e.g., expired gas flow, analysis of component gases, etc. Most measurement instruments are then susceptible to the formation of condensation. Since the instruments are generally in an environment colder than the temperature of the expired air, the risk of condensation is very high. Various types of dehumidifying devices have therefore been designed to capture or remove water vapor from the expired air without affecting the flow or composition of the gas.
One known device is described in U.S. Pat. No. 5,131,387. The device is formed by a container filled with a hydrophilic material in which a flow channel is arranged for the expired air. The hydrophilic material absorbs moisture as the moist expired gas flows past. A rod of hydrophilic material can also be arranged in the flow channel in order to improve moisture absorption.
A disadvantage of this known device is that it can only absorb a limited amount of moisture before it must be replaced. The replacement of the moisture-reducing device has two major disadvantages. Firstly, moisture absorption must be continuously monitored so that measurement or other functions are not interrupted when the moisture-absorbing material becomes saturated with moisture. Secondly, ambient air could be sucked into the gas system and affect measurements when the device is replaced. When anesthesia is being administered, anesthetic gas could also leak into the operating room when such a known moisture-absorbing device is replaced.
Another known type of dehumidifier is described in European Application 535 379. This dehumidifier is composed of a plurality of tubes, permeable to moisture, through which expired air passes. As a result of the difference in relative humidity between expired air and ambient air, moisture passes through the permeable tubes and is discharged into ambient air. This thereby reduces the relative humidity of expired air. The dehumidifier can be connected to existing tube systems and does not have to be replaced during its service life. The efficiency of this dehumidifier is due in part to the total area, permeable to moisture, and, in particular, the length of the permeable tubes. In certain situations, achieving a major reduction in relative humidity without extending the total length of tubing in the tube system is very desirable. A more compact dehumidifier than the described type would then be preferable in those circumstances.